This invention relates generally to a method for producing solid-state insulators, and more specifically to ion implanted insulators.
As used throughout this specification, the term "insulator" refers to a non-metallic solid state material with an apparent resistivity in excess of 10.sup.9 ohm-centimeter at room temperature. Prior efforts at creating electrically conductive regions within insulators have been ineffectual because of the difficulty inherent in "doping" an insulator. The prior efforts have been principally directed at doping by diffusion. Doping is usually understood to be the addition of a subtle (less than 1 in 10.sup.3) amount of impurity atoms to a solid to grossly change its electrical properties, while leaving other properties essentially unaltered. The purpose of diffusing dopants into an insulator is to produce impurity centers which can contribute charge carriers to the conduction process. However, this approach is seldom successful. Insulators are not, in general, amenable to being produced in a state of high purity, and hence a large background concentration of impurities is often present. In addition, the charge associated with impurities is often localized on the impurity site and, hence, cannot contribute to conduction. Amorphous insulators are an even more complex situation; large numbers of defect centers and unsatisfied bonds act to render a conventional doping approach unfeasible.
Ion implantation is the introduction of atoms into the surface layer of a solid substrated by bombardment of the solid with ions in the KeV to MeV energy range. The solid-state aspects are particularly broad because of the range of physical properties that are sensitive to the presence of a trace amount of foreign atoms. Mechanical, electrical, optical, magnetic, and superconducting properties are all affected and indeed may even be dominated by the presence of such foreign atoms. Use of implantation techniques affords the possibility of introducing a wide range of atomic species, thus making it possible to obtain impurity concentrations and distributions of particular interest; in many cases, these distributions would not be otherwise attainable. Recent interest in ion implantation has focused on the study of dopant behavior in implanted semiconductors and has been stimulated by the possibilities of fabricating novel device structures in this way. This is the common definition in the art. Implantation is within about the top 200 angstroms nearest the surface. A book which gives an overview of the implantation art as it relates to semiconductors is ION IMPLANTATION IN SEMICONDUCTORS, by James W. Mayer et al, 1970, Academic Press, New York, the entire disclosure of which is incorporated herein by this reference.
The inventive technique propounded herein, in contradistinction to the conventional doping approach, is to implant a massive local concentration of metallic ions in the insulator. Conduction occurs by the interaction of these implanted ions, either directly or in conjunction with the electronic environment provided by the host insulator.